River Murray operations 17-24 May 2017

26 May 2017

Welcome to our summary report on River Murray operations for the week ending 24 May 2017.

You can find the full weekly report under the River Murray system section of our website.

Rainfall and inflows

For the week ending 24 May 2017 moderate to heavy rainfall was recorded across the Basin. The majority of the Basin received rainfall between 15-50 mm, with totals in excess of 50 mm recorded in small pockets across Victoria, NSW and the ACT. A total of 93 mm was recorded at Mount Ginini on the border between NSW and the ACT and similar totals were also recorded over the NSW Snowy Mountains. Other significant totals occurred at Cooma, NSW, where 59 mm was recorded, and at locations in Victoria’s Wimmera district, where there were totals around 60 mm.

Widespread rain across the upper catchments saw a rise in stream flows along upper Murray tributaries. The Mitta Mitta River at Hinnomunjie bridge increased to 330 ML/day from around 260 ML/day. The upper Murray at Biggara saw a slightly higher boost in flow, increasing to almost 600 ML/day from 330 ML/day at the beginning of the week. The Ovens River, measured at Rocky Point, increased to almost 700 ML/day from around 500 ML/day. Stream flows have already began to recede as rainfall clears the region.

A chance of rain between 1-15 mm is currently forecast for the southern Basin and upper catchments of the River Murray in the next few days, which may result in another modest rise in stream flows.

Total in storage

The total MDBA storage increased by 54 GL this week, and total active storage is now 5,440 GL (63% capacity).

River operations

At Dartmouth Reservoir, the storage volume decreased by 1 GL to 3,004 GL (78% capacity). The release from Dartmouth, measured at Coleman’s, remained steady at just over 200 ML/day.

At Hume Reservoir, the storage volume increased by 53 GL to 1,929 GL (64% capacity). Releases from Hume Reservoir averaged about 950 ML/day during the week, peaking at almost 1,500 ML/day at the end of the week. Releases are currently being held at low levels to assist with the construction of erosion control works on the Dights Creek anabranch of the Murray between Hume Dam and Lake Mulwala. Dights Creek was enlarging rapidly as it captured increasing flow from the main channel of the River Murray. The works, Australia’s largest engineered log jam, will slow flow entering the anabranch, assisting the River Murray to remain as the primary channel.

Photo: Ben Berry, NSW Department of Primary Industries

Log jam construction on Dights Creek, an anabranch of the River Murray, downstream of Hume Reservoir.

At Lake Mulwala, the pool level is currently 124.71 m AHD. A slight decrease in the level is expected over this coming weekend with the levels between 124.6 and 124.7 m AHD likely during the next week. This is a temporary measure in response to decreased releases from Hume that are facilitating the engineering works at Dights Creek. The release downstream of Yarrawonga Weir has averaged around 3,500 ML/day with similar flow rates expected over the coming days.

Inflows have steadily declined on the Edward-Wakool system. Flows through the Edward River and Gulpa Creek offtakes are currently around 450 ML/day and 150 ML/day respectively. Flow downstream of Stevens Weir is currently around 530 ML/day. The weir pool is around 3.96 m AHD and will vary between 3.8 and 4.0 m over winter to provide connectivity for fish in the Yallakool and downstream in the Wakool Rivers. Visit the WaterNSW website for more information.

On the Goulburn River, the flow at McCoys Bridge is targeting 940 ML/day, with water above the minimum flow of 350 ML/day being provided for the environment. An environmental flow pulse for the Goulburn River is currently planned for late June. More information will be provided in future weekly reports. On the Campaspe River, the flow at Rochester is just over 40 ML/day.

On Tuesday 23 May, the Torrumbarry Weir pool began being drawn down. The pool is currently at 86.0 m AHD, or 5 cm below full supply level (FSL). In the coming weeks, as part of the weir pool variability program, the pool level is expected to be varied, with the level planned to decrease as much as 50 cm below FSL. Visit the MDBA website for more information. Diversions to National Channel were very low for much of the week, but have now been increased to around 450 ML/day to supply environmental flows along Gunbower Creek. Release downstream of Torrumbarry Weir remained steady and averaged around 4,000 ML/day.

Inflows from the Murrumbidgee River remained steady this week at around 400 ML/day (measured at Balranald). In coming weeks, inflows are expected to increase in response to recent rainfall in the upper Murrumbidgee catchment. Releases from Burrinjuck Dam increased to 4,000 ML/day this week in accordance with the water sharing plan for the Murrumbidgee regulated river. These ‘translucency’ releases are determined by rules in the water sharing plan and pass a proportion of the dam inflows in order to vary the flow downstream for the benefit of the riverine environment. There have also been small responses in tributaries downstream of Burrinjuck and Blowering Dams.

At Euston Weir, the pool level has remained around the FSL (47.60 m AHD). The flow rate downstream of the weir has averaged 6,000 ML/day and is likely to remain around this rate over the coming week.

On the Darling River, the total storage volume in the Menindee Lakes decreased by 3 GL and is currently 792 GL (46% capacity). This week the lakes have continued to receive inflows at low rates. A total of about 5 GL passed Wilcannia, with the daily flow continuing to recede (currently around 550 ML/day). Releases from Menindee Lakes to the lower Darling River at Weir 32 are currently around 400 ML/day. This is above the normal minimum of 200 ML/day at this time of year. The additional water is being released on behalf of environmental water holders to benefit native fish in the lower Darling River. Releases from Cawndilla outlet increased from 400 ML/day to 700 ML/day this week as part of the delivery of water to the Great Darling Anabranch for the benefit of native fish. These flows, which are also being delivered on behalf of environmental entitlement holders, are now being gradually wound back with rates around 100 ML/day expected by late June.

Downstream on the lower Darling River at Burtundy, the flow has remained around 300 ML/day.

At Lake Victoria, the storage level has varied between 24.40 m and 24.44 m AHD over the past two weeks. MDBA is currently targeting a lake level of 24.5 m AHD (395 GL) at the end of May in accordance with the Lake Victoria Operating Strategy. This end-of-May limit is applied in years when water remains available to MDBA in Menindee Lakes or when reserves held for NSW are in excess of 1,000 GL. From 1 June, MDBA will manage the filling of Lake Victoria so that the storage volume peaks as late in the year as possible. This strategy also aims to encourage the growth of foreshore vegetation and helps protect against erosional impacts on aboriginal cultural heritage, whilst maximising storage available to help supply flow to South Australia during next summer and autumn.

Flow to South Australia averaged 7,000 ML/day. The flow downstream at Lock 1 reduced from around 10,500 ML/day to 5,400 ML/day.

At the Lower Lakes, the 5-day average water level in Lake Alexandrina has increased to 0.65 m AHD. Barrage releases totalled around 58 GL this week as higher flows were released to assist in scouring sand around the Murray mouth. Releases through Mundoo, Tauwitchere and Goolwa barrages peaked around 14,000 ML/day with the release prioritised predominantly via Goolwa Barrage.